(require 'calendar)
(require 'cal-persia)
(defvar calendar-current-time-zone-cache nil
"Cache for result of calendar-current-time-zone.")
(defvar calendar-system-time-basis
(calendar-absolute-from-gregorian '(1 1 1970))
"Absolute date of starting date of system clock.")
(defun calendar-absolute-from-time (x utc-diff)
"Absolute local date of time X; local time is UTC-DIFF seconds from UTC.
X is (HIGH . LOW) or (HIGH LOW . IGNORED) where HIGH and LOW are the
high and low 16 bits, respectively, of the number of seconds since
1970-01-01 00:00:00 UTC, ignoring leap seconds.
Returns the pair (ABS-DATE . SECONDS) where SECONDS after local midnight on
absolute date ABS-DATE is the equivalent moment to X."
(let* ((h (car x))
(xtail (cdr x))
(l (+ utc-diff (if (numberp xtail) xtail (car xtail))))
(u (+ (* 512 (mod h 675)) (floor l 128))))
(cons (+ calendar-system-time-basis
(* 512 (floor h 675)) (floor u 675))
(+ (* (mod u 675) 128) (mod l 128)))))
(defun calendar-time-from-absolute (abs-date s)
"Time of absolute date ABS-DATE, S seconds after midnight.
Returns the pair (HIGH . LOW) where HIGH and LOW are the high and low
16 bits, respectively, of the number of seconds 1970-01-01 00:00:00 UTC,
ignoring leap seconds, that is the equivalent moment to S seconds after
midnight UTC on absolute date ABS-DATE."
(let* ((a (- abs-date calendar-system-time-basis))
(u (+ (* 163 (mod a 512)) (floor s 128))))
(cons
(+ a (* 163 (floor a 512)) (floor u 512))
(+ (* 128 (mod u 512)) (mod s 128)))))
(defun calendar-next-time-zone-transition (time)
"Return the time of the next time zone transition after TIME.
Both TIME and the result are acceptable arguments to current-time-zone.
Return nil if no such transition can be found."
(let* ((base 65536) (quarter-multiple 120) (time-zone (current-time-zone time))
(time-utc-diff (car time-zone))
hi
hi-zone
(hi-utc-diff time-utc-diff)
(quarters '(2 1 3)))
(while (and quarters (eq time-utc-diff hi-utc-diff))
(setq hi (cons (+ (car time) (* (car quarters) quarter-multiple)) 0))
(setq hi-zone (current-time-zone hi))
(setq hi-utc-diff (car hi-zone))
(setq quarters (cdr quarters)))
(and
time-utc-diff
hi-utc-diff
(not (eq time-utc-diff hi-utc-diff))
(let* ((tail (cdr time))
(lo (cons (car time) (if (numberp tail) tail (car tail))))
probe)
(while
(let* ((lsum (+ (cdr lo) (cdr hi)))
(hsum (+ (car lo) (car hi) (/ lsum base)))
(hsumodd (logand 1 hsum)))
(setq probe (cons (/ (- hsum hsumodd) 2)
(/ (+ (* hsumodd base) (% lsum base)) 2)))
(not (equal lo probe)))
(if (eq (car (current-time-zone probe)) hi-utc-diff)
(setq hi probe)
(setq lo probe)))
hi))))
(defun calendar-time-zone-daylight-rules (abs-date utc-diff)
"Return daylight transition rule for ABS-DATE, UTC-DIFF sec offset from UTC.
ABS-DATE must specify a day that contains a daylight savings transition.
The result has the proper form for calendar-daylight-savings-starts'."
(let* ((date (calendar-gregorian-from-absolute abs-date))
(weekday (% abs-date 7))
(m (extract-calendar-month date))
(d (extract-calendar-day date))
(y (extract-calendar-year date))
(last (calendar-last-day-of-month m y))
(candidate-rules
(append
(list (list 'list m d 'year))
(if (< d 8)
(list (list 'calendar-nth-named-day 1 weekday m 'year)))
(if (> d (- last 7))
(list (list 'calendar-nth-named-day -1 weekday m 'year)))
(let (l)
(calendar-for-loop j from (max 2 (- d 6)) to (min d (- last 8)) do
(setq l
(cons
(list 'calendar-nth-named-day 1 weekday m 'year j)
l)))
l)
(if (and (= m 3) (<= 20 d) (<= d 21))
'((calendar-gregorian-from-absolute
(calendar-absolute-from-persian
(list 1 1 (- year 621))))))
(if (and (= m 9) (<= 22 d) (<= d 23))
'((calendar-gregorian-from-absolute
(calendar-absolute-from-persian
(list 7 1 (- year 621))))))))
(prevday-sec (- -1 utc-diff)) (year (1+ y)))
(while
(let ((rules candidate-rules)
new-rules)
(while
(let*
((rule (car rules))
(date
(cond ((eq (car rule) 'calendar-nth-named-day)
(eval (cons 'calendar-nth-named-absday (cdr rule))))
((eq (car rule) 'calendar-gregorian-from-absolute)
(eval (car (cdr rule))))
(t (let ((g (eval rule)))
(calendar-absolute-from-gregorian g))))))
(or (equal
(current-time-zone
(calendar-time-from-absolute date prevday-sec))
(current-time-zone
(calendar-time-from-absolute (1+ date) prevday-sec)))
(setq new-rules (cons rule new-rules)))
(setq rules (cdr rules))))
(setq candidate-rules (if new-rules (nreverse new-rules)
(list (car candidate-rules))))
(setq year (1+ year))
(cdr candidate-rules)))
(car candidate-rules)))
(defun calendar-current-time-zone ()
"Return UTC difference, dst offset, names and rules for current time zone.
Returns (UTC-DIFF DST-OFFSET STD-ZONE DST-ZONE DST-STARTS DST-ENDS
DST-STARTS-TIME DST-ENDS-TIME), based on a heuristic probing of what the
system knows:
UTC-DIFF is an integer specifying the number of minutes difference between
standard time in the current time zone and Coordinated Universal Time
(Greenwich Mean Time). A negative value means west of Greenwich.
DST-OFFSET is an integer giving the daylight savings time offset in minutes.
STD-ZONE is a string giving the name of the time zone when no seasonal time
adjustment is in effect.
DST-ZONE is a string giving the name of the time zone when there is a seasonal
time adjustment in effect.
DST-STARTS and DST-ENDS are sexps in the variable `year' giving the daylight
savings time start and end rules, in the form expected by
`calendar-daylight-savings-starts'.
DST-STARTS-TIME and DST-ENDS-TIME are integers giving the number of minutes
after midnight that daylight savings time starts and ends.
If the local area does not use a seasonal time adjustment, STD-ZONE and
DST-ZONE are equal, and all the DST-* integer variables are 0.
Some operating systems cannot provide all this information to Emacs; in this
case, `calendar-current-time-zone' returns a list containing nil for the data
it can't find."
(or
calendar-current-time-zone-cache
(setq
calendar-current-time-zone-cache
(let* ((t0 (current-time))
(t0-zone (current-time-zone t0))
(t0-utc-diff (car t0-zone))
(t0-name (car (cdr t0-zone))))
(if (not t0-utc-diff)
(list nil nil t0-name t0-name nil nil nil nil)
(let* ((t1 (calendar-next-time-zone-transition t0))
(t2 (and t1 (calendar-next-time-zone-transition t1))))
(if (not t2)
(list (/ t0-utc-diff 60) 0 t0-name t0-name nil nil 0 0)
(let* ((t1-zone (current-time-zone t1))
(t1-utc-diff (car t1-zone))
(t1-name (car (cdr t1-zone)))
(t1-date-sec (calendar-absolute-from-time t1 t0-utc-diff))
(t2-date-sec (calendar-absolute-from-time t2 t1-utc-diff))
(t1-rules (calendar-time-zone-daylight-rules
(car t1-date-sec) t0-utc-diff))
(t2-rules (calendar-time-zone-daylight-rules
(car t2-date-sec) t1-utc-diff))
(t1-time (/ (cdr t1-date-sec) 60))
(t2-time (/ (cdr t2-date-sec) 60)))
(cons
(/ (min t0-utc-diff t1-utc-diff) 60)
(cons
(/ (abs (- t0-utc-diff t1-utc-diff)) 60)
(if (< t0-utc-diff t1-utc-diff)
(list t0-name t1-name t1-rules t2-rules t1-time t2-time)
(list t1-name t0-name t2-rules t1-rules t2-time t1-time)
)))))))))))
(calendar-current-time-zone)
(defvar calendar-time-zone (or (car calendar-current-time-zone-cache) -300)
"*Number of minutes difference between local standard time at
`calendar-location-name' and Coordinated Universal (Greenwich) Time. For
example, -300 for New York City, -480 for Los Angeles.")
(defvar calendar-daylight-time-offset
(or (car (cdr calendar-current-time-zone-cache)) 60)
"*Number of minutes difference between daylight savings and standard time.
If the locale never uses daylight savings time, set this to 0.")
(defvar calendar-standard-time-zone-name
(or (car (nthcdr 2 calendar-current-time-zone-cache)) "EST")
"*Abbreviated name of standard time zone at `calendar-location-name'.
For example, \"EST\" in New York City, \"PST\" for Los Angeles.")
(defvar calendar-daylight-time-zone-name
(or (car (nthcdr 3 calendar-current-time-zone-cache)) "EDT")
"*Abbreviated name of daylight-savings time zone at `calendar-location-name'.
For example, \"EDT\" in New York City, \"PDT\" for Los Angeles.")
(put 'calendar-daylight-savings-starts 'risky-local-variable t)
(defvar calendar-daylight-savings-starts
(or (car (nthcdr 4 calendar-current-time-zone-cache))
(and (not (zerop calendar-daylight-time-offset))
'(calendar-nth-named-day 1 0 4 year)))
"*Sexp giving the date on which daylight savings time starts.
This is an expression in the variable `year' whose value gives the Gregorian
date in the form (month day year) on which daylight savings time starts. It is
used to determine the starting date of daylight savings time for the holiday
list and for correcting times of day in the solar and lunar calculations.
For example, if daylight savings time is mandated to start on October 1,
you would set `calendar-daylight-savings-starts' to
'(10 1 year)
If it starts on the first Sunday in April, you would set it to
'(calendar-nth-named-day 1 0 4 year)
If the locale never uses daylight savings time, set this to nil.")
(put 'calendar-daylight-savings-ends 'risky-local-variable t)
(defvar calendar-daylight-savings-ends
(or (car (nthcdr 5 calendar-current-time-zone-cache))
(and (not (zerop calendar-daylight-time-offset))
'(calendar-nth-named-day -1 0 10 year)))
"*Sexp giving the date on which daylight savings time ends.
This is an expression in the variable `year' whose value gives the Gregorian
date in the form (month day year) on which daylight savings time ends. It is
used to determine the starting date of daylight savings time for the holiday
list and for correcting times of day in the solar and lunar calculations.
For example, if daylight savings time ends on the last Sunday in October:
'(calendar-nth-named-day -1 0 10 year)
If the locale never uses daylight savings time, set this to nil.")
(defvar calendar-daylight-savings-starts-time
(or (car (nthcdr 6 calendar-current-time-zone-cache)) 120)
"*Number of minutes after midnight that daylight savings time starts.")
(defvar calendar-daylight-savings-ends-time
(or (car (nthcdr 7 calendar-current-time-zone-cache))
calendar-daylight-savings-starts-time)
"*Number of minutes after midnight that daylight savings time ends.")
(defun dst-in-effect (date)
"True if on absolute DATE daylight savings time is in effect.
Fractional part of DATE is local standard time of day."
(let* ((year (extract-calendar-year
(calendar-gregorian-from-absolute (floor date))))
(dst-starts-gregorian (eval calendar-daylight-savings-starts))
(dst-ends-gregorian (eval calendar-daylight-savings-ends))
(dst-starts (and dst-starts-gregorian
(+ (calendar-absolute-from-gregorian
dst-starts-gregorian)
(/ calendar-daylight-savings-starts-time
60.0 24.0))))
(dst-ends (and dst-ends-gregorian
(+ (calendar-absolute-from-gregorian
dst-ends-gregorian)
(/ (- calendar-daylight-savings-ends-time
calendar-daylight-time-offset)
60.0 24.0)))))
(and dst-starts dst-ends
(if (< dst-starts dst-ends)
(and (<= dst-starts date) (< date dst-ends))
(or (<= dst-starts date) (< date dst-ends))))))
(defun dst-adjust-time (date time &optional style)
"Adjust, to account for dst on DATE, decimal fraction standard TIME.
Returns a list (date adj-time zone) where `date' and `adj-time' are the values
adjusted for `zone'; here `date' is a list (month day year), `adj-time' is a
decimal fraction time, and `zone' is a string.
Optional parameter STYLE forces the result time to be standard time when its
value is 'standard and daylight savings time (if available) when its value is
'daylight.
Conversion to daylight savings time is done according to
`calendar-daylight-savings-starts', `calendar-daylight-savings-ends',
`calendar-daylight-savings-starts-time',
`calendar-daylight-savings-ends-time', and
`calendar-daylight-savings-offset'."
(let* ((rounded-abs-date (+ (calendar-absolute-from-gregorian date)
(/ (round (* 60 time)) 60.0 24.0)))
(dst (dst-in-effect rounded-abs-date))
(time-zone (if dst
calendar-daylight-time-zone-name
calendar-standard-time-zone-name))
(time (+ rounded-abs-date
(if dst (/ calendar-daylight-time-offset 24.0 60.0) 0))))
(list (calendar-gregorian-from-absolute (truncate time))
(* 24.0 (- time (truncate time)))
time-zone)))
(provide 'cal-dst)